Spark plug



Patented Feb. 14, 1950 UNITED STATES PATENT oFFlcE SPARK PLUG Rex J. L. Dutterer, Hastings, Mich., assigner to lhlstlngs Manufacturing Company, Hastings,

Application July 17, 1946, Serial No. 684,161

3 Claims. (Cl. 123--169) 'I'his invention relates to improvements in spark plugs. f

'I'he principal objects of this invention are:

First, to provide a tight seal around the center electrode of a spark phg which is not affected by the engine gases and temperature changes involved in the operation of an internal combustion engine.

Second, to provide a spark plug with a sectional center electrode which may be effectively sealed to the walls of the insulator and which will not transmit mechanical stresses to the insulator due to temperature variations in the insulator.

Other objects relating to details and economies of the invention will appear from the description to follow. The invention is defined and pointed out in the claims.

The drawings of which there is one sheet illustrate a preferred form of the invention and two spark plugs embodying modified forms of the invention.

Fig. 1 is a vertical cross-sectional view through a spark plug embodying the invention.

Fig. 2 is an elevational view partially in crosssection of an insulator having a modified form 2 end of the electrode to the terminal. The lower end of the center electrode is similarly connected to the head II on the lowerelectrode as at Il.

Positioned around the center electrode and against the upper end cf the lower electrode is a capillary tube I8 which is formed of glass, preferably of a boro-silicate composition. The tube I8 defines a center capillary passage which is just large enough to pass the center electrode I5. The tube I8 forms a gas tight seal in the center bore of the insulator, and in order to facilitate sealing of the tube to the walls of the bore, the walls are glazed as at I9.

The materials forming the tube I8 and center electrode I5 are chosen to have approximately the same coeilicient of expansion to prevent unequal expansion from breaking the seal between the center electrode and the glass tube. It will be noted that the center electrode extends for a portion of its length through the bore without lateral support so that any variation in length of the center electrode relative to the length of the bore may be absorbed or compensated for by bending of the electrode in its unsupported portion. The center electrode being made of fine of the invention embodied therein. 'o wire to pass through the capillary tube, this Fig. 3 is an elevational view partially in crossbending 0f the electrode wm not, apply any apsection, having a second modified form of the preciable Stress to the insulator. invention embodied therein. In assembling the electrodes in the insulator Fig. 4 is an elevational View partially in CTOSS- 0 the center electrode is first electrically secured section 0f the Sealing member used in Figs. 1, 2, to the lower electrode by one of the previously and 3. explained methods, and the two are passed down- The reference character I indicates the sleeve wardly in the bore of the insulator until the head member of a Spark plug that iS DIOVded With a I I engages the shoulder at the top of the rethreaded portion 2 fOr installation in an engine 35 duced portion 0f the b01e The capillary 'tube and a side electrode 3. The ceramic insulator 4 is then threaded over the center electrode and is secured within the sleeve I by crimping over pushed downwardly against the head I I, The the rim 5 t0 clamp the Sealing rings 6 tightly assembly is then heated until the glass tube I 8 around the shoulders formed on the outer surface reaches a softening or plastic stage at which of the insulator ln the well known manner- 40 time a hollow tool is passed into the bore and The insulator defines a central bore 'I which around the center electrode I5 to rmly press 1S provided With a 10Wer DOftOn 3 0f redlleed and deform the tube into all openings and spaces cross section and an upper Portion 9 which iS within the bottom of the bore and rmly into internally threadedsealing engagement with the glazed walls of the The lower portion of the bore is arranged to 4,-, bore and the center electrode. The upper termireceive the lower electrode I0 which projects benal I2 is then fitted over the upper end 0f the low the lower end 0f the iDSUIatOI and which 1S center electrode and screwed into the threaded provided with a collar II arranged to engage the portion 9 of the bore and the connection I6 beshoulder at the upper end of the reduced portion tween the tcp cf the terminal and the center of the bOle- All Upper terminal l2 is arranged -,0 electrode is completed. The insulator assembly to have a screw connection with the threaded is then ready to be joined with the sleeve I in portion 9 of the bore and is provided with a any of the well known manners. head I3 engageable with the top of the insulator In the modified form of plug shown in Fig. 2, t0 limit the distance to which the terminal may a packing 2n formed of ceramic cement interbe screwed into the bore. The upper terminal 5,3 mixed with finely divided powdered metal such I2 defines a fine central aperture I4 arranged to as nickel or molybdenum or powdered metal pass the centerelectrode I5 which is made of alone is interposed around the lower end of the fine wire. The upper end of the center electrode center electrode I5 and between the lower end is electrically connected to the upper terminal of the capillary glass tube I8 and the collar on I 2 as at I8 by crimping, peening, or weldingA the G0 the lower electrode I0. In assembling thespark plug, the deforming of the capillary 4tube I8 will also compact the metal or the packing mixture against the upper end of the lower electrode to increase the heat conductivity to the insulator around the lower electrode. In other respects, the insulator assembly shown in Fig.2 is the same as the preferred form of assembly shown in Fig. 1.

In the modified form of insulator assembly shown in Fig. 3 the lower electrode 2I is provided with a cup-shaped portion 22 at its upper end which fits snugly within the bore 1 of the insulator. The mixture of cement and powdered metal is positioned in the cup-shaped portion 22 and around the lower end of the center electrode I5 as is indicated at 23. The capillary glass tube I8 is pressed firmly against the cement and metal mixture and the upper end of the cupshaped portion 22 in the operation of compressing and deforming the tube. If desired, the cement and metal mixture may extend above the cup 22. In other respects the insulator assembly is the same as the preferred form shown in Fig. 1.

As `explained before, the insulator assembly wlil not be subjected to mechanical strains due to the expansion'of the electrodes because of the small diameter and unsupported length of the center electrode I5. At the same time a continuous metallic connection is maintained between the upper terminal and the lower electrode 8, and the center bore of the spark plug is effectively sealed by compacting the capillary tube while in a soft state tightly into sealing contact with the center electrode and the glazed walls of the central bore.

The invention has been illustrated and described in embodiments which have been found to be highly satisfactory. No attempt has been made to Lshow other possible adaptations, as it is believed that this disclosure will enable those skilled in the art to embody the invention as may be desired.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A spark plug comprising an insulator member dening a smooth walled central bore with a lower portion of reduced cross-section and an internally threaded portion at the top thereof, a lower electrode provided with an enlargement engaging the bottom of the upper portion of said bore and extending beyond the bottom of said insulator, acenterelectrode formed of fine wire electrically `and mechanically connected to the top of said enlargement and extending upwardly beyond the top of said insulator, a terminal tip passed over the upper end of said wire and having threaded connection with the threaded portion of said bore, said terminal tip having an enlargement engaging the top of said insulator whereby the lower end of said tip does not extend beyond the threaded portion of said bore, the upper end of said wire being mechanically and electrically connected to the top of said terminal, and a preformed capillary tube of boro-silicate glass positioned around the lower end of said center electrode and snugly fitting the walls of said bore, the walls of said bore being glazed where they contact said tube and being fused to said tube, said tube terminating substantially below said tip.

2. The method of manufacturing spark plugs including an insulator dening a smooth walled central bore with a reduced portion at the lower end thereof and an internally threaded portion at the top thereof, and a lower electrode having a shoulder at the upper end thereof which comprises the steps of, electrically and mechanically connecting a iine wire to the top of said lower electrode, introducing said lower electrode into said bore until said shoulder engages the top of said reduced portion, introducing a preformed tube of boro-silicate glass having a capillary opening therethrough into said bore with said wire threaded through said opening, said tube closely fitting the central portion of said bore, heating the insulator thus far assembled to soften said glass and compressing said tube against said shoulder and the walls of ysaid bore, the walls of said bore being glazed adjacentto said tube, passing a terminal member having a capillary opening therein over the upper end of said wire and threading said terminal into the threaded upper end of said bore, said terminal having a ange engageable with the end of said insulator to locate said terminal axially with respect to said bore and electrically connecting the upper end of said wire to the top of said terminal, said tube being substantially shorter than the central portion of said bore whereby a 'substantial portion of said wire below said terminal is laterally unsupported.

3. The method of manufacturing spark plugs including an insulator defining a smooth walled central bore with a reduced portion at the lower end thereof and an internally threaded portion at the top thereof, and a lower electrode having a shoulder at the upper end thereof which comprises the steps of, electrically and mechanically connecting a fine wire to the top of said lower electrode, introducing said lower electrode into said bore until said shoulder engages the tcp of said reduced portion, introducing a preformed tube of glass having a capillary opening therethrough into said bore with said wire threaded through said opening, said ube closely tting the central portion of said bore, heating the insulator thus far assembled to soften said REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS y Date Number Name 2,047,302 Xardell July 14, 1936 2,246,948 McCarty June 24, 1941 2,293,381 Carington Aug. 18, 1942 2,301,686 y Doran Nov. 10, 1942 2,317,305 Schwartzwalder Apr. 20, 1943 2,349,432 Hopps May 23, 1944 2,380,579 Cipriani July 31, 1945 2,406,966 Pfeil Sept. 3, 1946 

